The present invention is related to the field of antennas, and more particularly to a monopole antenna provided for short-range applications, and comprising an electrically conductive pattern arranged on a dielectric substrate.
In the ever-increasing use and development of wireless communication, the demand for small and compact portable devices is likewise increasing. The miniaturization is possible owing to the rapidly reducing physical size and cost of wireless electronic components, this in turn enabled by the progress and technological improvements made in microelectronic technologies, such as semiconductors, packaging and interconnection technologies.
Antennas constitute a crucial part of such wireless communication system, but have not been subject to a corresponding cost and size reduction. The physical size of an antenna is not as much related to the improvements of the manufacturing methods used, as to the operating frequency or wavelength of the system in which it is to be used. Accordingly, as portable devices, such as mobile phones, become smaller and smaller, new requirements are placed on miniaturizing the antennas to be used with such devices as well. However, making antennas smaller include several challenges, as the performance of the antenna should not be allowed to decrease. The cost of the antenna is also a very important consideration, especially in short-range wireless communication devices.
Classical antenna structures such as monopoles and dipoles are fabricated using dedicated structural components such as wires, tubes and mechanical support. This is an expensive manufacturing method and would add far too much cost to equipment for short-range wireless communication applications, such as Bluetooth enabled equipment, in order to be feasible.
For short-range antennas to be cost-effective, they are instead manufactured by high volume, low cost manufacturing technologies similar to the methods used for manufacturing the microelectronic components themselves. Examples of such manufacturing technologies include ceramic multilayer antennas and printed antennas, that is, antennas made by PCB (Printed Circuit Board) technology.
There are integrated antennas available, for example patch antennas and microstrip antennas manufactured by PCB, ceramic technologies or by utilising special low dielectric materials. Such antennas, although having a relatively low cost, have a physical height much exceeding current requirements.
Even the classical antenna configurations monopole and dipole antennas may be manufactured by printed circuit board techniques. However, the operating frequency of the antenna should be so high that the physical size of the antenna is reasonable with respect to the manufacturing technology. This gives a physical size of the antenna many times bigger than the size of the radio component itself, which is of course unacceptably large.
A type of antenna resembling a printed monopole antenna is a printed inverted F antenna (PIFA), the physical size of which is somewhat smaller, but still very big compared to the typical component size.
Still another type of antenna typically made by PCB technology is a loop antenna. The physical size of a loop antenna can be reduced by introducing additional components, such as capacitors, but at the expense of reduced performance. Besides the additional space required, the addition of components also adds time to the manufacturing process, and entails another possible source of failure. Further, the radiation efficiency of loop antennas is rather low.
Still another type of antenna is a fractal antenna, first described about a decade ago. It is based on so-called fractal geometries, or geometrical patterns repeating itself in smaller and smaller size. The major advantage of fractal antennas is their ability to operate on a wide range of frequencies, and it is also possible to design compact fractal antenna structures. However, the fractal geometrical patterns are often very complex and can therefore be difficult to manufacture with high precision.
Thus, all the above described antenna types entail shortcomings regarding their suitability to be miniaturised as well as to be easily integrated, and it would therefore be desired to provide an antenna structure overcoming these difficulties.